BUTLER, United States, July 14, 2024 (BSS/AFP) - Donald Trump on Sunday called for Americans to unite after he was injured in an assassination attempt, a dark new chapter in the US presidential race that set an already polarized nation on edge.

The 78-year-old former president was hit in the ear at a campaign rally in Butler, Pennsylvania, while the shooter and a bystander were killed and two spectators critically injured in the worst act of US political violence in decades.

With the country reeling from scenes of a bloodied Trump being rushed away by Secret Service agents, reports emerged that the shooter, identified as 20-year-old Thomas Matthew Crooks, also had explosives in his car.

"In this moment, it is more important than ever that we stand United," Trump said in a statement on his Truth Social network, adding that Americans should not allow "Evil to win."

The Republican added that it was "God alone who prevented the unthinkable from happening" and that he would "FEAR NOT."

Trump's wife Melania said the gunman was a "monster," who had attempted to silence her husband's "laughter, ingenuity, love of music, and inspiration."

President Joe Biden has already condemned the attack as "sick" and spoke to Trump afterwards.

Biden was due to give further remarks at the White House on Sunday, after top security officials including the chiefs of the FBI and Secret Service briefed him and Vice President Kamala Harris.

- Security questions -

Questions are swirling about the motive of shooter Crooks, whose body was seen in television images on a low roof of a building, near a weapon understood to have been an AR-15 style semiautomatic rifle.

Investigators had found explosive material in his car parked near the scene, US media said, while the FBI also searched his house.

The shooter, reportedly a registered Republican, was believed to be working alone.

His father Matthew Crooks told CNN that he was trying to establish "what the hell is going on."

The shooter had an account on the secure internet server Discord but a spokesman said it was "rarely utilized and we have found no evidence that it was used to plan this incident, promote violence, or discuss his political views."

The shocking incident also drew criticism of security at the rally, particularly about how a presidential candidate could be targeted by a gunman around 150 meters away despite a huge Secret Service detail.

US Secret Service spokesman Anthony Guglielmi rejected "absolutely false" claims that it had refused additional protection for Trump ahead of the rally.

A local prosecutor said Sunday it was "surprising" that a shooter was able to position himself on the nearby rooftop to take his shot.

- Shockwaves -

The attempt on Trump's life sent shockwaves around the world, but the effects on a tight US presidential race in a deeply divided country will take time to play out.

Trump's family has already been promoting images of the president raising a defiant fist to the crowd after the shooting.

Trump clutched his ear and fell to the ground after shots rang out at the rally on Saturday, his last appearance before the Republican National Convention in Milwaukee.

Secret Service agents surrounded him then bundled the former president off stage with blood streaked across his ear and face.

Trump said that he was "shot with a bullet that pierced the upper part of my right ear" and heard a "whizzing sound."

His narrow escape has sparked conspiracy theories and fingerpointing by Republicans. Possible Trump vice presidential pick J.D. Vance claimed Biden's campaign "rhetoric" had "led directly" to the attack.

US politics have become increasingly hostile, with Trump building his image around inflammatory verbal assaults, and many Democrats expressing fury and disgust at Trump's rise.

World leaders condemned the attack, with the Kremlin on Sunday morning saying there was no place for violence in politics and the Vatican denounced what it called an "injury to democracy."

The spectator who died was named as Corey Comperatore.

"The hatred for one man took the life of the one man we all love the most," his sister told US media. "We watched him die on the news."

The United States has a history of political violence. President John F. Kennedy was assassinated in 1963 while President Ronald Reagan was shot but survived an assassination attempt in 1981.